JP3228733B2 - Superconducting film formation method - Google Patents

Description

The present invention relates to a method for forming a superconducting film, comprising forming a superconducting film at a high critical temperature on a ceramic substrate and suppressing a chemical reaction between the substrate and the superconducting film. For the purpose of ensuring performance, a metal film (buffer layer) having a multilayer structure is formed on a ceramic substrate at a predetermined temperature, and a superconducting film is formed on the metal film at a predetermined temperature.

[Industrial applications]

The present invention relates to a method for forming a superconducting film, and more particularly, to a method for forming a buffer layer having a multilayer structure on a ceramic substrate and forming an oxide superconductor wiring on the buffer layer.

[Conventional technology]

As a method for forming wiring on a ceramic substrate as a wiring substrate for interconnecting electronic elements used in an electronic device or the like, a thin film is formed on a substrate by vapor deposition or the like, and a wiring pattern is formed by an etching technique. And a method of forming a thick film pattern by forming a printed pattern on a substrate by printing a paste containing a wiring conductor as a main component by a printing technique, and the like.

As materials for this film, not only normal conductors such as Cu and Mo, but also Nb,
Y-Ba-Cu-O system (MKWu, LRAshburn, CJTrong, PH
Hor, RLMeng, L. Gao, ZJHuang, YQWang, and CWC
hnu: Phy. Rev. Lett., 58 , (1987) 908) and Bi-S.
r-Ca-Cu-O system (H.Maeda, Y.Tanaka, M.Fukutomi, and
T. Asano: Jpn. J. Appl. Phys. 27 (1988) L209) and the Bi-Pb-Sr-Ca-Cu-O system reported by Takano et al. (M. Takano, J. Takada, K. Oda) , H.Kaitaguchi, Y.Miura, YI
keda; Y.Tomii, and H.Mazaki: Jpn.Appln.Phys: 27 (198
8) Refer to L1041). However, when a film of a conductor material such as a normal conductor or a superconductor is formed on a substrate, due to an interaction such as a chemical reaction between the film and the substrate,
In some cases, the target substance could not be obtained with a uniform composition, and in particular, the performance of the superconductor could not be exhibited.

On the other hand, there is known a superconducting film device that is apparently similar to the superconducting film obtained by the method of the present invention (Japanese Patent Publication No. 63-279521). In other words, this apparatus forms a metal film having a thermal expansion coefficient larger than 10 × 10 ⁻⁶ / K on a ceramic substrate, and forms a bevelskite-type metal oxide superconducting film on the metal film. A film is formed. This conventionally known invention is different from the object of the method of the present invention in that the conductor layer of a metal having a predetermined coefficient of thermal expansion is formed as a ceramic substrate in order to prevent the occurrence of cracks in the coating of the superconductor itself. It is interposed between the superconductor layer.

Japanese Unexamined Patent Publication No. Sho 63-305574 (published on December 13, 1988) discloses a superconductor substrate for forming a superconductor on a support substrate. A superconductor substrate characterized in that a composite material is formed by interposing a stabilizer which does not chemically react with the superconductor. However, JP-A-63-305574 discloses that a Pf, Pd, Ag, Au film is formed on an Al ₂ O ₃ substrate by vapor deposition, sputtering, thermal spraying, plating, etc., and a Y-Ba-Cu-O-based superconducting film is formed thereon. No idea is given to form a body film and to form a plurality of the above-mentioned metal films as a stabilizer.

Accordingly, this prior art differs from the object and configuration of the present invention.

[Problems to be solved by the invention]

An object of the present invention is to form a uniform superconductor film by suppressing or preventing a chemical reaction between a ceramic substrate and a superconductor film.

Still another object of the present invention is to form or prevent two or more metal layers between the ceramic substrate and the superconductor film by a predetermined method to suppress or prevent the occurrence of pinholes in the metal layers. Aim.

[Means for Achieving the Object, Functions and Effects of the Invention]

The purpose of the present invention is to solve the above problems. To achieve this object, the present inventors have conducted intensive studies, and as a result, in order to suppress a chemical reaction between the substrate and the superconductor film, a buffer material that does not easily react with the substance of the superconductor film was used. The present inventors have found that it is effective to form a plurality of layers between the superconductor films by a predetermined method, thereby completing the present invention.

That is, the present invention relates to a method for forming a group Ib (copper group:
Cu, Ag, Au) or Group VIII (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt)
Forming a metal film of the above, further forming an oxide superconducting film on the metal film, wherein the metal film is a metal film having a multilayer structure of two or more layers of the same or different metal layers, Further, the formation of the metal film is performed by firing a coating film of the raw material paste at a higher temperature than the formation of the superconducting film, and the formation of the superconducting film is performed in a temperature range in which a superconductor crystal is grown. It is characterized in that it is performed by baking the coating film of the raw material paste.

Hereinafter, the present invention will be further described with reference to the accompanying drawings.

As apparent from the above description, the present invention provides a step of forming two or more multilayer metal films (buffer layers) on a ceramic substrate such as an alumina substrate or a Y ₂ O ₃ stabilized zirconia substrate, Forming a film of an oxide superconductor on the film. Each of the steps will be described below.

In the step of forming two or more multilayer metal films, the following materials are used as the material of the metal film. That is,
As a material of the first metal film formed on the ceramic substrate, a metal belonging to Group IB or an element having the same crystal structure as that of Group IB and having atomic numbers adjacent to each other, for example, an iron group (Fe, Co, Ni) or metals belonging to the platinum group (for example, Pd, Pt) are used. Further, a metal that can bond to a Group IB metal via oxygen, for example, Cr or the like can also be used.

Next, the metal constituting the second metal film formed on the first metal film may be any metal that is easily adhered to the metal of the first metal film. Specifically, the metal of the second metal film may be any one of the above-mentioned metals, and may be the same metal or a different metal. As the metal layer element, an element which hardly affects the oxide superconductor substance or an element which does not affect the development of the superconducting phase even if substituted slightly can be used. As metal layer element
When Cu, Fe, Co, Ni, or the like is used, the firing atmosphere for forming the metal layer is an inert gas atmosphere. Since the baking atmosphere for forming the superconductor layer is baking in an oxidizing atmosphere such as the air, the surface layer of the metal layer may be oxidized, but the baking atmosphere reacts with the superconductor material formed thereon. Anything that does not need to be used.

This metal film is formed by printing, drying and baking a paste (not including frit glass) consisting of only an organic substance and metal powder on a ceramic substrate, for example, an alumina substrate. After firing, the same or different metal paste is similarly printed and fired on the previously fired metal film to produce an alumina substrate having two or more metal layers. This metal layer acts as a buffer layer.

An oxide superconducting substance or a composition thereof is deposited on the buffer layer and heat-treated to obtain a superconducting film.

Even if you find a metal film substance that does not easily react with a superconducting substance, it alone will
It has been found that the formation of superconductors may be hindered.

That is, it is essential that the firing temperature in forming the metal film is higher than the sintering temperature of the oxide superconductor. this is,
When the sintering temperature for forming the metal film is about the same as or lower than the sintering temperature of the oxide superconductor, the energy state near the surface of the metal constituting the metal film (which is mainly used for sintering) becomes high-temperature sintering This is because it may be higher than in the case of. In this case, during the heat treatment of the oxide superconductor, the metal in the metal film causes mass transfer, the composition of the superconducting film fluctuates, and the superconductivity manifests. Further, it is necessary to form the superconducting film within a temperature range in which a superconductor crystal is grown.

If the sintering is performed outside these ranges, the crystal growth of the superconducting material is not good, and a superconducting phenomenon having an intended critical temperature cannot be obtained.

Furthermore, in order to produce a high-temperature superconducting film having good superconducting properties, it is sometimes preferable to set a temperature at which the superconducting film melts during heat treatment. At this time, if there is a pinhole in the buffer layer, a part of the composition for obtaining the molten superconductivity moves toward the ceramic substrate and the composition shifts, so that a good superconducting film cannot be obtained.

That is, in the method of the present invention, the metal layer (buffer layer) is formed in a multilayer structure of two or more layers, and the firing temperature for forming the metal layer is performed at a temperature higher than the firing temperature of the oxide superconductor. There is no diffusion of superconducting material into the buffer layer and then the substrate during firing of the superconducting film (ie, mass transfer to the buffer layer and the substrate is suppressed or prevented) and a good superconducting layer is formed. It is considered that this is because generation of pinholes in the buffer layer is prevented and grain boundary pores in the buffer layer are reduced. The firing temperature for forming the superconducting film on the substrate is selected from the temperature range in which the superconductor crystal grows as described later. Therefore, the temperature range differs depending on the system constituting the superconductor.

 Hereinafter, the present invention will be described with reference to examples.

〔Example〕

Example 1 FIGS. 1 and 2 show the outline steps of the method of the present invention. FIG. 1 shows a manufacturing process of a substrate with a metal film, and FIG. 2 shows a process of forming a superconducting film on an alumina substrate.

 This will be further described below.

99. Purity of 99.7% purity on an Al ₂ O ₃ substrate with an average particle size of 1 μm.
An Ag paste consisting of 9% or more of Ag powder and a vehicle of organic matter (solvent and organic resin; 0.8 parts by weight of the organic resin is 100 parts by weight of the Ag powder) was printed.
After drying the printed circuit board at 110 ° C, 800-970 in air
Calcination was carried out for 10 minutes under various conditions at a temperature of ° C. Ag fired
An Ag paste was printed on the film in the same region, dried, and fired to form a substrate with a metal film (FIG. 1). In this case, if the thickness is smaller than several μm, the formed metal layer becomes uneven. Therefore, the thickness of the metal layer formed by one baking is several μm or more, preferably 10 μm or more in order to suppress the generation of pinholes. The thickness of the entire metal layer obtained by printing and firing the metal layer a plurality of times was 20 μm or more. In this embodiment, the thickness of the Ag layer formed by one firing is 10 μm,
By applying and baking the Ag paste twice, an Ag layer having a thickness of 20 μm was formed.

In the case of using a substrate fired at 800 ° C. to fire the metal layer, when the firing of the superconducting film described below was performed, the component of the superconducting material reached the alumina substrate through the Ag film. On the other hand, when a substrate fired at 900 ° C. to 955 ° C. was used to fire the metal layer, the diffusion of the component of the superconducting material into the alumina substrate was not detected in the firing described below. When the metal layer is baked at about 960 ° C. or more, Ag melts out and does not form a film on the substrate due to surface tension.

As shown in FIG. 1, a substrate obtained by firing twice at a high temperature to form a plurality of metal layers on the substrate was used for the next step.

 The high-temperature superconducting film was formed as follows.

In the Bi-Pb-Sr-Ca-Cu-O system (however, the amount of final pb was very small or not detected), a bulk of a high-temperature superconductor having a critical temperature of 110K class was produced. Bi−Pb−
As an example of the composition of the Sr-Ca-Cu-O system, Bi _0.7 Pb _0.3 Sr
A composition ratio of ₁ Ca ₁ Cu _1.8 O _9.15 was used. This bulk sample was roughly pulverized in a mortar, and further pulverized in a ball mill to obtain a powder having an average particle diameter of about 10 μm or less. This powder and a vehicle composed of an organic substance were mixed and kneaded to prepare a paste containing Bi-Pb-Sr-Ca-Cu-O-based powder as a main component. This paste was printed on an alumina substrate without a buffer layer, and an alumina substrate with a metal film fired at about 900 ° C. to form a metal layer, and then dried.
A substrate printed using a paste of a superconducting substance (or a superconducting forming substance) was fired in the air to produce a substrate with a superconducting film (see FIG. 2).

The firing temperature is selected from a temperature range in which a superconductor crystal is grown.

The thickness of the formed superconductor layer is 5 to 100 μm, though it depends on the screen printing mesh. In this embodiment, a superconductor layer of about 80 μm was formed.

In the case of the Bi-Pb-Sr-Ca-Cu-O system, the firing temperature is 830 to 860C. Therefore, in this example, as shown in Table 1 below, firing was performed at 870 ° C. (Comparative Example 1) and 840 ° C. (Examples 1 to 4). Comparative Example 2 is an example having no Ag metal film.

As a result of X-ray diffraction measurement using a Cu K line, the sample of Comparative Example 1 was found to be Bi—Sr—Cu—O having Ag and Tc of about 10 K on the film surface.
Superconducting phase, CaO, CuO detected, Bi-Pb-Sr-Ca-Cu-
High T of O-based superconductors with a critical temperature of 80K to 110K class
No c-phase crystal peak was detected.

References regarding other Bi-Sr-Cu-O superconducting phases are as follows: (1) J. Akimitsu, A. Yamazaki, H. Sawa and H. Fujiki;
nJAppl.Phys. 26 (1987) L2080.

(2) C. Michel, M. Hervien, HMBorel, A. Grandin, F. Des
landes, J. Provost and B. Raveau: Z. Phys. B 68 (1987) 42
1.

FIG. 3 shows X-ray diffraction patterns of the samples of Examples 1 to 4. In each of these samples, peaks of low Tc phase and high Tc phase crystals of a superconductor having a critical temperature of 80K to 110K were detected. When the sintering time was 1,6,50 hours, the peak of the corresponding superconducting crystal having a critical temperature of 110K tended to increase when the sintering time increased, and the tendency tended to decrease when the sintering time was 90 hours. . FIG. 4 shows an example of a temperature-dependent measurement result of the electrical resistivity of each sample of Examples 2 to 4. The sample of Example 3 was a superconducting film having a Tce (TC endpoint) of about 90K. In the sample of Comparative Example 2, a reaction with the substrate was observed, and no transition to superconductivity was observed.

Example 2 An example using a partially stabilized Y ₂ O ₃ -zirconia substrate as a ceramic substrate will be described.

Printing on a zirconia substrate Ag powder consisting of Ag powder with an average particle diameter of 1 μm and purity of 99.9% or more and an organic vehicle, drying at 110 ° C., and baking in air at a temperature between 900 and 960 ° C. for 10 minutes . On the fired Ag film in the same way
After printing and drying the Ag paste, it is fired to produce a zirconia substrate having two metal layers. On the other hand, Bi-Pb-Sr-
A bulk of a high temperature superconductor having a critical temperature of 110K class in a Ca-Cu-O system is produced. After this bulk sample is assembled and ground in a mortar, it is further ground in a ball mill, and the average particle diameter is about 10 μm.
Make the following powder. This powder and a vehicle composed of an organic substance were mixed and kneaded to prepare a paste containing Bi-Pb-Sr-Ca-Cu-O-based powder as a main component. This paste is printed and dried directly on the zirconia substrate and on the metal layer of the zirconia substrate having two metal layers, and then dried in air.
Bake at 840-860 ° C.

The sample printed, dried, and fired directly on the zirconia substrate has poor adhesion to the substrate, and has a Bi-Pb-Sr-Ca-Cu-O
The film is easily peeled off, and the resistance remains around 77K. On the other hand, a sample obtained by printing a paste of a superconducting substance (or a superconducting forming substance) on a metal layer, drying and firing is Bi-Pb-Sr-
The Ca-Cu-O film is hardly peeled off, and becomes a superconducting film having a Tco of about 110K and a Tce of about 90K.

Example 3 An Au paste was used as a metal layer instead of a silver paste,
A circuit board having a superconductor layer wiring pattern was prepared in the same steps as in Example 1 except that the Au paste printed board was fired at 900 ° C., and the same results as in Example 1 were obtained.

The example in which the metal layer has a two-layer structure has been described above. However, a third metal film made of a metal having adhesion to the second metal is further formed on the second metal film to form a three-layer structure. It is also possible to use a buffer layer having a structure.

Since the present invention is configured as described above, a superconducting thick film having a high critical temperature can be formed using ceramics as a substrate. Also, since the normal metal is used as the buffer layer, this buffer layer can be used as a medium that maintains a good connection between the normal conductor and the superconducting film, and as a result, the performance of the required conductor is exhibited. It works.

[Brief description of the drawings]

FIG. 1 is a process diagram showing one embodiment of the present invention, FIG. 2 is a process diagram showing one example of the production of a substrate with a metal film in the present invention, and FIG. 3 is obtained by the method of the present invention. FIG. 4 is an X-ray diffraction pattern diagram of the sample obtained. FIG. 4 is a graph showing the temperature dependence of the electrical resistivity of the sample obtained by the method of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Niwa 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-1-248696 (JP, A) JP-A-1-286920 (JP, a) JP Akira 64-72410 (JP, a) JP Akira 64-27294 (JP, a) JP Akira 63-305574 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ H01L 39/22-39/24 H01L 39/00 H01B 12/06 H01B 13/00 H05K 3/24

Claims (1)

(57) [Claims] 1. A method for forming a superconducting film made of an oxide superconductor on a ceramic substrate, comprising: forming a group Ib (copper group) or V
Applying a raw material paste containing a Group III metal, repeating the firing of the obtained coating film at a temperature higher than the sintering temperature used for forming the superconducting film, from the same or different metals Forming a metal film having a multilayer structure of two or more layers, and applying the raw material paste of the superconducting film on the ceramic substrate via the metal film having the multilayer structure, A method for forming a superconducting film, comprising a step of sintering within a temperature range for growing a conductor crystal.